Not Applicable
Not Applicable
1. Field of Invention
This invention relates generally to vertical and short takeoff and landing (VSTOL) vehicle, specifically to an improved VSTOL vehicle that is stable and capable of high speed cruise with ducted rotors wherein the ducts remain stationary and at angles between the vertical and longitudinal axes of the vehicle, and the thrusts from the ducted rotors are adjustable and vectored.
2. Description of Prior Art
Ducted rotors, also known as ducted fans, are more efficient and quieter than exposed propellers of the same diameters. They are also safer than exposed propellers on the ground.
Several designs have involved ducted rotors to achieve VSTOL with high-speed cruise capability. The designs have included separate fans for vertical and horizontal thrust (see U.S. Pat. No. 5,890,441); ducted fans mounted in the fixed wings which rotate from horizontal to vertical (see U.S. Pat. No. 3,335,977). These designs suffer from inefficient redundancy, or heavy and complex mechanism that is prone to failure, particularly during transition from hover to flight and vice versa.
A more recent design has four ducted fans fixed on both sides of the fuselage and mounted parallel to the longitudinal axis of the fuselage, with exit vanes in each ducted fan to redirect airflow for vertical takeoff and landing (see U.S. Pat. No. 5,115,996). The design was intended to achieve efficient high-speed cruise. On closer look, however, such compromise makes vertical take-off inefficient as ninety degree thrust vectoring during takeoff causes significant power loss just when the thrust and power are most needed. Thus bigger ducted fans and more powerful engines are required, which actually produces more drag at high-speed cruise. Four big fans drawing in air from the front also pose significant safety hazard on the ground. Noise can easily escape from both the front and aft ends of the ducts. Stability control during transition from hovering to forward flight can also be very challenging.
Yet another recent design example is the DuoTrek by Millennium Jet Inc., which has four shallow (depth of the duct substantially smaller than the rotor diameter) ducted fans mounted horizontally on both sides of the fuselage. The design has only a very moderate top speed, as the horizontally mounted and shallow ducted fans are not efficient for high-speed cruise. Noise level will also be necessarily high as the ducts are too shallow to provide much shield.
Therefore several objects and advantages of the present invention are:
(a) to provide a VSTOL design that presents a better compromise between the conflicting requirements of vertical take off and high speed cruise.
(b) to provide a VSTOL design that is inherently more stable and easier to control during all phases of flight, particularly during the transition between hover and forward flight which has been particularly challenging to previous designs.
(c) to provide a VSTOL design that takes full advantage of the potential benefits of ducted rotors;
(d) to provide a VSTOL design that is more efficient in reducing drag and power requirements during all phases of flight.
(e) to provide a VSTOL design that is safe with multiple measures for emergency landing.
(f) to provide a VSTOL design that is quiet.
(g) to provide a VSTOL design that is compact, versatile and capable of multiple use, including meeting motor vehicle requirements to drive on local streets and highways;
(h) to provide a VSTOL design that is capable of flying close to ground much as a hovercraft to take advantage of the ground effect.
Still further objects and advantages will become apparent from a consideration of the ensuing description and drawings.
In accordance with the present invention, a preferred embodiment includes a fuselage with two pairs of ducted rotors fully enclosed fore and aft of the fuselage respectively, and two vertical stabilizers attached to the fuselage. The fuselage is configured to generate aerodynamic lift in forward flight. All four ducts are configured such that their center axes are at angles tilted sufficiently forward from the vertical axis of the fuselage. Each ducted rotor is powered by one engine inside the duct behind the rotor.
In the preferred embodiment of the present invention, all four rotors and engine shafts rotate counterclockwise, generating substantial angular momentum with gyroscopic effect. Variable-shape inlets of the ducted rotors and vector thrusting of the airflow out of the ducted rotors combine to provide efficient power and control during vertical flight.